How to add a new field to existing XML Mapping

Hi, everyone! Good day!

I've made an XML file which I imported to my doc using XML Mapping Pane -> (Add new part...) and I used it to map some texts.

Imported XML fields

Fields being used as Plain Text Content Control

How could I add new fields to this XML Mapping?

What I tried:

I tried editing the XML file and then importing it again. As a result, I have two XML Mappings with the same name that act as completely separate mappings. I couldn't even find a way to delete the older one.